In distillation, absorption, gas scrubbing and like process operations, columns are used which contain baffling for the heat exchange and mass transfer between liquid and gas. These baffles are either comprised of trays, like for example bell trays, tunnel trays, dual flow trays, sieve trays or bubble trays, as randomly distributed packing bodies, like for example Raschig rings, Pall rings or saddles, or as ordered packings. With ordered packings, geometries of a cross channel or cross flow structure are widely used for technical applications. Commercially available types are for example the Montz A3, BSH and B1 types of Montz GmbH, D-40705 Hilden, the Sulzer BX, CY and Mellapak types of Sulzer Chemtech AG, CH 8404 Winterthur, the FLEXIPAC type of Koch-Glitsch, Wichita, Kans. 67208 (USA) and the intalox type of Norton, Akron, Ohio 44309 (USA).
With solid internal and packing columns, it is necessary to ensure the greatest possible uniformity of the distribution of liquid and gas over the column cross section in order to obtain a high separating efficiency. The uniform distribution of the gas can be realized simply since the unavoidable pressure loss in the solid internals and packings by themselves ensure a largely uniform distribution of the gas stream over the column cross section and which for most technical applications is sufficient.
With fixed bed reactors as well, there is the problem of uniform distribution of liquids over the reactor cross section to avoid local overheating, so-called hot spots, from arising. It has thus been found to be advantageous to use distribution devices for the liquid.
The uniform distribution of liquids over the column cross section can be achieved only with difficulty. Special distributors for the liquid are necessary. In the art, a number of distributors constructions are available which operate based upon the principles of damming up of liquids, free overflow or spraying. In K. Sattler: “Thermal Separating Processes” (1988), VCH Verlagsgesellschaft mbH, D-69451, Weinheim, there is found at pages 226 to 231 an overview of technologically useable distributor constructions.
The simplest form of liquid distribution is found in the edge deflector as is described in U.S. Pat. No. 3,099,697, the liquid being guided away from the column wall and being released at some distance from the column wall again. There is no description as to how the liquid trickling density can be made uniform in the remaining regions of the column cross section.
In part, nozzles are used to distribute the liquid over the column cross section. The distribution quality which can thus be achieved is however limited so that this distribution principle is useable only with simple observations or gas scrubbing.
Spreaders are distributors in which the liquid to be distributed from a container which is open upwardly, usually branched channels which extend over the column cross section, over overflow devices.
These overflow devices are comprised, for example, of serrated weirs and must be oriented precisely horizontally in order to ensure a uniform liquid distribution over the column cross section. In a similar manner tubes with openings at their underside can distribute the liquid over the cross section covered by the tube system. Here as well the tubes must be oriented as closely horizontally as is possible.
Since these precisely horizontal orientations can be achieved in practice only with difficulty with the requisite precision, one utilizes distributor systems, in applications with greater requirements as to distribution quality, which operate based upon the damming-up principle. Here the liquid flows out of the channels not over overflow weirs but over narrow openings in the lower regions of the channels. Since the operating state of the liquid damming-up height as a rule amounts to between 0.05 to 0.15 m, the imprecision with respect to horizontal orientation of the distributor device is not as significant as those which operate by the overflow principle. The fabrication cost is, however, significantly higher. Examples of these constructions are EP 374 443 B1, EP 462 048 B1, EP 462 049 B1, EP 434 510 B1, DE 19 615 645 A1, U.S. Pat. No. 4,476,069, U.S. Pat. No. 5,501,079, U.S. Pat. No. 5,192,465 and U.S. Pat. No. 5,518,667.
With very high requirements for the distribution quality, special constructions are used which, in addition to the damming up of the liquid, utilizes the capillary distribution effect. Examples are described in EP 512 277 B1 and U.S. Pat. No. 4,432,913.
Another principle for obtaining a high distribution quality is the intermittent actuation of individual distribution points for the liquid. An example is found in U.S. Pat. No. 4,776,989.
In U.S. Pat. No. 4,569,364 a distributor is described which can be adjusted externally in a targeted manner.
U.S. Pat. No. 5,776,316 describes a collection and distribution device which additionally enables liquid to be exchanged in a targeted manner over the column cross section.
In U.S. Pat. No. 5,387,377, a structurally expensive device is described in which an effort is made to use the distribution device additionally as a mass-exchange element. The parts of the device through which gas flows contains packing which support the mass exchange and which determines the gas throughput through the remaining mass-exchange elements.
A similar effect is described in U.S. Pat. No. 5,695,548. Here a collection of distribution channels, which are arranged in a multiplicity of layers above one another, is traversed in uniflow by gas and liquid. This improves the mass transfer.
Distributors must be provided in packed columns and solid internal columns at the head of the column for distributing the refluxed liquid as well as at all feed locations for the liquid feed. Additionally it is customary with large separations, such numbers of a column to provide intermediate distributors for the liquid. These intermediate distributors suppress the disadvantageous effects of poor distribution of the liquid as in the case of edge flow or stream flow.
The need for liquid distributors is an important economic requirement in the use of solid internal and packing columns. Especially the redistribution of the liquid is expensive in the column 1 since the liquid which flows out of the mass-transfer packing and is to be redistributed is initially collected in a liquid collector 2 via a collecting trough 3 and guided to a downcomer pipe 4 and the liquid distributor 5 (FIG. 1). The minimum height for the total assembly of collection trough, downcomer tubes and the distributor, even with smaller column diameters, is about 1 m and with large-column diameters is normally 1.5 to about 2 m. Since a plurality of these devices are necessary in a column, this gives rise to an increase in the column height by about 25% and higher capital costs.
With liquid mixtures with phase breakdown in the liquid phase, difficulties arise in that usual distributor construction cannot reliably ensure uniform distribution of the two liquid phases over the column cross section. In the case of phase breakdown, it is usually best to initially separate both liquids in phase-separating only and then to introduce them via two separate distribution systems.